The present invention relates to a wheel alignment measurement apparatus for measuring in particular the alignment data of wheels of a 4-wheel vehicle by means of measuring heads and evaluation means.
From the German Patent 29 34 411 a wheel alignment measurement apparatus is known. Therein six angle measurement instruments are used of which one instrument is arranged at each wheel of a 4-wheel vehicle and two further instruments are mounted on the ends of support arms, such support arm being fixed to the front wheels and protruding beyond the front wheels in direction of travel of the vehicle. Through a calculation circuitry the angles measured by means of the angle measurement instruments can be evaluated to that extent that the individual track of the wheels and the total track of the front and rear wheels, respectively, can be found. Said German patent discloses no means for determining the inclination of the wheels and thus for determining the camber, castor and king pin inclination of the wheels of a 4-wheel vehicle.
From the German disclosure letter 35 31 459 a wheel alignment measurement apparatus and a wheel alignment measuring method for vehicles are known, in which the required data for an adjustment and/or alignment system, respectively, for vehicle wheels are delivered by a plurality of measuring heads mounted on the vehicle wheels, providing wheel data and being of such construction that they may be arranged at the vehicle wheels in a predetermined correlation with respect to the wheels. Said German disclosure letter discloses a measuring head comprising an infra-red transmitter and/or receiver, respectively, for measuring horizontal angles, the receiver consisting of a diode line of twenty to thirty diodes. Thus, the measuring heads mounted on the wheels can be optically correlated with one another and the data required for detecting the track values can be found. For simultaneously finding the values of inclination of the wheels common inclination measurement instruments are comprised in the measuring heads and all data are evaluated in a central processing unit. With this apparatus all wheel alignment data can be found. It is, however, necessary to effect an evaluation of different sensors, this resulting in a complex control and evaluation by the central processing unit and causing cumbersome installment and adjustment operations. Due to the use of different sensors also different error sources will be present and--as well--different constructions of the measuring heads for the respective wheels will be required and, thus, this will result in an overall uneconomical kind of construction.